In general, the signal providing apparatus currently equipped in an aircraft is an audio tuner contained in the arm of each seat with headphones connected with the tuner that allow the passenger to listen to the signal. Lately, the number of aircraft equipped with a video monitor which can provide video data, has increased. In such aircraft, it is necessary to reduce the weight and volume of equipment in order to increase the number of passengers that can be carried. The weight and the volume of the cable for transmitting data for the signal providing apparatus is relatively large because the cable is connected through controllers and receivers to all of the monitors and headphones which are equipped in each of the seats. It is accordingly useful to reduce the weight of such cable for the purpose of reducing the total weight of the equipment. In addition, a number of seats, often three for example, are formed from one box seat in the aircraft. In order to attach such box seat, a long dented rail is used and the cable for the signal apparatus lies inside the rail, for which entrance is covered with a lid from the outside. Since the cross-sectional size of the rail is relatively small, it is impossible to pass anything other than cables having small diameters through it.
For the above reason, the diameter of the cable used for the signal providing apparatus is limited in size. In addition, since the signal providing apparatus transmits an analog signal for a video image which has a bandwidth limited to 8 MHz, in other words, to one channel of a television signal, it can provide a maximum of only 20 channels. Thus, use of the signal providing apparatus is limited, as is described below. For example, the signal providing apparatus provides, at maximum, only 20 channels for pre-viewing movies for in-flight sales of video tapes. Such limited number of channels is insufficient to suit the tastes of many passengers and the in-flight sales of video tapes is not profitable. Since the number of the channels that can be delivered by the signal providing apparatus in the prior art are small, sale of in-flight videos is similarly limited. Although it is possible to transmit a baseband signal as digital data of a video image, the cost of modifying the circuits of the apparatus, in other words, of changing the transmission rate, is high when the number of channels is increased. Such signal providing apparatus would require an encoder for outputting a video image through a TV tuner or a TV camera in real time. Such an encoder is large, heavy and expensive.